The present invention relates to devices for transmitting and receiving data in a digital telecommunication system, as e. g. a base station or a mobile terminal, and to a method for transmitting and receiving random access bursts in a random access channel of a digital telecommunication system.
In a telecommunication system, data are communicated between base stations and mobile stations. Thereby, the communication area is divided in cells, in which one base station communicates with one or more mobile stations. The data transmission from a mobile station to a base station is called uplink and the data transmission from a base station to one or more mobile stations is called downlink. For the uplink and the downlink, several transmission channels for the transmission of control and user data are available, e. g. a broadcast control channel, a synchronization channel, a user data channel, a random access channel etc. In some telecommunication systems, a communication also between mobile terminals is possible.
A communication device of the telecommunication system, as e. g. a base station or a mobile terminal, may not have an existing dedicated connection to another communication device of the telecommunication system, but may wish to start the transmission of control or user data. An example of such data may be an initial setup message to be sent from a mobile terminal to a base station to establish a first signaling connection. Usually, the random access channel is used for this purpose since it does not require prior negotiation, whereby the random access channel is accessed randomly by the communication device (usually a mobile terminal) requiring a connection. Thereby, the random access data transmitted from a mobile station to a base terminal can e. g. contain a request, if the base station has sufficient resources available to build up the required connection or to transfer user data.
Usually, a random access burst consists of a preamble part and a message part as shown in FIG. 1. The preamble part may have a length of 1 ms, and the message part may have a length of 10 ms, whereby a time delay is present between the preamble part and the message part.
The random access channel used for the transmission of the random access bursts comprises or consists of succeedingly or periodically provided random access time windows, in which several random access slots are available. The different random access slots are randomly chosen by a communication device for the transmission of random access data. E. g. in a currently proposed wide band direct sequence CDMA (WCDMA) system, the random access channel is based upon an initial preamble spreading code. The spreading code for each cell needs to be planned to ensure that neighboring cells do not use the same preamble spreading code. Within the preamble part of each random access burst, is provided the preamble signature code, which is one of a number of separate codes, i. e. 16, available for use within that cell. These separate preamble signature codes can be seen as separate slots, as indicated in the scheme shown in FIG. 2, in which 16 separate preamble signatures are shown as an example. One of these preamble signature codes is chosen randomly by a communication device for the transmission of the preamble part of the random access burst.
Beforehand, the base station or the respective cell controlling unit signals, e. g. over the broadcast control channel, which codes are available in each cell. Additionally, within the time frame for the transmission of a random access burst (10 ms) are provided a number of time offsets, each of 1.25 ms allowing a further 8 variations. In other words, in each time frame a random access time window is provided, a scheme of which is shown in FIG. 2 and which comprises a plurality of random access slots for transmitting random access data. The random access time window thereby extends over a time frame of 10 ms, so that 128 different random access slots (16 separate preamble codes and 8 time offsets) are provided within one random access time windows. It is to be noted that the above-mentioned numbers are only used as examples and other numbers can be chosen depending on system requirements.
The preamble signature code, i. e. the signature code of the preamble part of a random access burst determines the spreading code for the message part of this random access burst. As shown schematically in FIG. 3, the preamble signature points to a place in the spreading code tree available for the message part. The message part is then transmitted with this spreading code, e. g. with a spreading factor 16 or 32. Thus, the possibility of collisions between message parts simultaneously transmitted from different communication devices is significantly reduced.
In FIG. 4, a sequence of exchanged data between a first communication device, i. e. a user equipment or mobile terminal, and a second communication device, i. e. a cell controller or a base station of the telecommunication system is schematically shown.
The mobile terminal attempting to transmit random access data in the random access channel firstly transmits the preamble part to the base station. The preamble part, as explained above has an allocated unique combination of a preamble signature and a time offset randomly chosen from the available values. Thus, a collision of two preamble parts simultaneously sent from two different mobile terminals to a receiving base station only occurs if the two preamble parts have the same preamble signature and the same time offset. A base station properly receiving a preamble part transmits an acquisition response, e. g. on a downlink common channel, back to the mobile terminal. By means of the acquisition response, the base station signals to the mobile terminal that it is expecting the message part. Then, the mobile terminal transmits the corresponding message part to the base station. In case that the base station does not send an acquisition response, the message part is not sent. The message part contains the random access data. Since the length of the message part is fixed, e. g. 10 ms, the amount of data to be transmitted within one message part is restricted. However, in many cases the size of the message part of the random access burst will be insufficient, so that the random access data to be transmitted have to be segmented over a number of different random access bursts. The transmission of a number of random access bursts is problematic since the transmission is contention-based and there is an increased possibility of collisions when a number of random access bursts is transmitted sequentially. Further, this leads to an undeterminable duration for the random access data transmission. Further, for each random access data segment, a new random access burst has to be formed and to be transmitted. Further, each preamble part has to be successfully received in a receiving device and answered by a positive acquisition response so that the corresponding message part can be transmitted. Then, the random access data of the different message parts transmitted within the different random access bursts have to be reassembled in the receiving device into the complete data set.
The object of the present invention is therefore to provide devices for transmitting and receiving data in a digital telecommunication system and a method for transmitting and receiving random access bursts in a random access channel of a digital telecommunication system, which enable the transmission of a larger amount of random access data in a simple and efficient way.
The above object is achieved by a device for transmitting and receiving data in a digital telecommunication system, in which a random access channel for transmitting random access bursts is provided, with generating means for generating a random access burst comprising a preamble part for acquiring a part of said random access channel and at least one message part for transmitting data in said acquired part of said random access channel, the number of message parts depending on an amount of data to be transmitted in the message parts, whereby in case that two or more message parts are generated, the generating means generates said random access burst with at least one continuation indicator indicating said two or more message parts, and transmitting means for transmitting the random access burst generated by said generating means. This device according to the present invention is e. g. a mobile terminal of the telecommunication system.
Thus, the device according to the present invention enables the transmission of large amounts of random access data in a random access burst by providing several message parts within one random access burst. After the transmission of a preamble part and the corresponding acquisition response from a receiving device, several message parts can be transmitted without the necessity to transmit a preamble part for each transmitted message part. The random access burst contains an continuation indicator which informs the receiving device that the random access burst comprises more than the usual one message part. The receiving device, e. g. a base station of the communication system, then reserves a part of the random access channel, e. g. on the basis of the spreading code of the message part which is determined by the signature code of the preamble part, so that an undisturbed reception of the succeeding message part(s) is assured. Another communication device attempting to access the random access channel with a preamble part having the same signature code will not receive an acquisition indicator from the receiving device during the reservation period. Once the access to the random access channel is granted, a transmitting communication device according to the present invention is able to transmit a large amount of random access data within a plurality of message parts without the risk that the access to the random access channel is refused due to contention.
Advantageously, the generating means generates a random access burst comprising two or more message parts so that a continuation indicator is contained in at least the first message part. Thereby, the continuation indicator may contain information on how many message parts are comprised in the random access burst.
In the first advantageous example of a device transmitting a random access burst according to the present invention, the generating means generates a random access burst comprising two or more message parts so that each preceding message part comprises a continuation indicator indicating an immediately succeeding message part. Thereby, the generating means may further advantageously generate a random access burst comprising two or more message parts so that the last of the message parts comprises an end indicator indicating the message part to be the last message part. Thereby, the continuation indicator and/or the end indicator may be located at the end of the respective message part. This enables to maintain the normal structure of the message parts, since the continuation indicator and/or the end indicator is just added to the end of the message part. Further, the continuation indicator and/or the end indicator may consist of a single bit in the respective message part. Hereby, a receiving device can decide in a simple way if a further message part will follow. Advantageously, the continuation indicator as well as the end indicator may consist of a single bit and have different bit values, which enables simple processing structures on the transmitter side and on the receiver side.
In a second advantageous example of a device transmitting a random access burst according to the present invention, the random access channel comprises a number of random access slots being divided into a first section containing contention-based random access slots and a second section containing reservation-based random access slots, whereby the transmitting means transmits the preamble of a random access burst comprising two or more message parts in said second section. Thereby, a receiving device receiving the preamble in the second section knows that the corresponding burst will comprise two or more message parts. This is particularly advantageous since a receiving device receiving a preamble part in the second section may immediately reserve a further part of the random access channel for the receiving of the second message part after the reception of the usual first message part. In this case, the generating means further advantageously generates the preamble of a random access burst comprising two or more message parts by randomly choosing one of the random access slots of the second section, whereby a preamble signature code allocated to the chosen random access slots serves as a continuation indicator indicating that a second message part will be transmitted after the first message part. This is particularly advantageous in a code division multiple access (CDMA) system, in which the signature code of a preamble part of a random access burst determines the spreading code of the succeeding message part since a receiving device is then able to reserve the further part of a random access channel in a simple way. Further advantageously in this case, the generating means generates a random access burst comprising three or more message parts so that each first message part out of three immediately succeeding message parts comprises a continuation indicator indicating that the third message part will be transmitted after the second message part.
In this way, the receiving device knows in due time that a further message part will be transmitted after the immediately succeeding message part and is thus able to reserve a corresponding part of the random access channel.
A device for receiving random access bursts according to the present invention comprises receiving means for receiving a random access burst comprising a preamble part for acquiring a part of said random access channel and at least one message part for transmitting data in said acquired part of said random access channel, the number of message parts depending on an amount of data to be transmitted in the message part, detecting means for detecting a continuation indicator in a received random access burst, said continuation indicator indicating that said random access burst comprises at least two message parts and reserving means for reserving a further part of said random access channel for receiving said message parts upon detection of said continuation indicator.
Advantageously, the detecting means is adapted to detect the continuation indicator in at least a first received message part. The continuation indicator may contain information on the number of message parts contained in the random access burst. Further advantageously, the reserving means, upon detecting said continuation indicator in a received message part, reserves a further part of said random access channel for an immediately succeeding message part. Thereby, only the corresponding part of the random access channel for receiving the very next message part is reserved. Further advantageously, the detecting means is further adapted to detect an end indicator in a received message part, said end indicator indicating the message part to be the last message part of at least two message parts, whereby the reserving means terminates the reservation of the random access channel upon the detection of said end indicator.
In case that the random access channel comprises a number of random access slots being divided into a first section containing contention-based random access slots and a second section containing reservation-based random access slots, the reserving means of the receiving device of the present invention, reserves, after the reception of a preamble part of a random access burst in said second section, a further part of the random access channel for receiving at least two message parts. Upon reception of a preamble part in said second section, the receiving device therefore knows that at least one second message part after the usual first message part will be transmitted. In this case, the detecting means, after the reception of a preamble part of a random access burst in said second section, treats the preamble signature code of the preamble part as the continuation indicator indicating that a second message part will be transmitted after the first message part, whereby the reserving means reserves a further part of said random access channel for receiving said second message part. The reserving means may thereby reserve the further part of the random access channel by blocking out the preamble signature code of the received preamble part, i. e. by not sending an acquisition indicator upon a reception of a preamble part having the same signature code from another transmitting device.
Further advantageously, the reserving means, upon detection of a continuation indicator in a received message part of the random access burst, reserves a further part of said random access channel for receiving a further message part of the immediately succeeding message part. Thereby, in case that the random access burst comprises three or more message parts, the necessary parts of the random access channel can be reserved in due time.
The proposed communication devices and the proposed method of the present invention are particularly advantageous, since they support the use of a random access burst having a standard length, i.e. the proposed scheme is backward compatible. In the case that the continuation indicator is the last bit of the message part and this bit is set to zero, the message part corresponds to a standard length message part.
Further advantageously the two or more message parts are continuously, i.e. directly one after the other, transmitted and received. Hereby, a very efficient transmission of message parts can be achieved.